FRONT SIGHT: I got the Williams Firesights (fiber optic front and rear), but was disappointed in the small dia. light pipe they used in the front so I drilled it out just a little to accept a fatter and brighter EGW "big dot" light pipe and I love it now.
SPRING KITS: Wolff will sell and deliver an multi-spring pack to you for around $15. Use the link below to go to the GP100 Shooter's Pak
http://gunsprings.com/1ndex.html
Installation is quick and easy, it can really improve the double action pull.